This invention relates to apparatus used in nuclear imaging and more particularly to a gantry and pallet assembly having at least one scintillation camera for conducting whole body or single photon emission computed tomography (SPECT) scans.
Medical technology has developed methods and apparatus which harness radiopharmaceuticals to provide images of a preselected region of the human body that has been made temporarily radioactive. The radiopharmaceutical introduced into the human body selectively accumulates within the region of interest. The radiation emitted by the radiopharmaceutical is detected by one or more scintillation cameras which are used to map the distribution of the radioactively tagged pharmaceuticals. The scintillation camera collects data representative of the radiation emitted by the radiopharmaceutical; the collected data is then used to reconstruct images corresponding to selected transverse planes through the region of interest as shown in U.S. Pat. No. 4,057,727 issued to Muehllehner et al. on Nov. 8, 1977 which is hereby specifically incorporated by reference.
Conventional images have an inherent limitation in that underlying and overlying radioactivity distributions are often superimposed upon the region of interest resulting in images having poor contrast. SPECT imaging eliminates this problem by obtaining multiple views about the patient and using appropriate computer software to generate images of the cross-sectional slices of the region of interest. This is accomplished by either continuously or incrementally rotating at least one scintillation camera around a patient while maintaining the camera close to the patient's body and substantially perpendicular to that region of the patient's body from which data is being collected. For example, as many as 360 views could be obtained if the scintillation camera was incrementally rotated one degree at a time to acquire a complete data set. It is common to rotate the cameras in increments of three degrees resulting in 120 acquisition points. Incremental rotation requires that the scintillation camera be held stationary at each incremental position while data collection takes place.
For more rapid data collection, the scintillation camera can be continuously rotated about the patient and data collected in separate images corresponding to preselected angular increments. This method is not as accurate as incremental rotation for detailed examinations.
When diagnostic rotational SPECT scanning is performed the patient lies on an arcuate narrow table, customarily known as a pallet, which conforms to the patient's body so the detectors can get as close to the patient as possible. Whole body scanning does not require camera head rotation but does require that the detector be translated over the patient's body in linear fashion. It is important that a detector passing above the patient lying on his or her back follows the contour of the patient's body thereby staying close to it. Because no rotation is required the patient lies on a pallet which is wider than the one used for SPECT scanning thereby providing more comfort to the patient. Moreover, the pallet should be flat so a detector passing underneath the patient can get as close to the patient's body as is needed for that particular scan.
Additionally, when conducting a rotational SPECT scan, the amount of time needed to conduct the scan decreases with the number of detectors used. Thus, it may be cost effective and easier on the patient to use two or three detector heads instead of just one when performing a scan.
Rotational SPECT imaging can be performed over any part of a patient's body. Thus, it is necessary to orient the scintillation camera or cameras relative to a pallet so they can be rotated around the region of interest. Additionally, present diagnostic procedures are such that it is economically and practically advantageous to utilize imaging apparatus capable of performing both rotational SPECT scanning and whole body scanning. Thus, the scintillation cameras must be able to translate the length of a patients body as well as rotate around it any point along its axis.
In one commercially available system, the Siemens Rota Camera, a gantry is provided having a through hole of sufficient size to allow a patient supported on a pallet to pass at least part way therethrough. The through hole has a rotation ring mounted therein with two diametrically arranged detectors connected thereto a distance away from the rotation ring. The detectors are capable of being rotated in a plane perpendicular to the longitudinal axis of the through hole. The gantry has arranged therewith an automatically driven bed which can be longitudinally translated through the through hole to conduct a whole body scan. One disadvantage with this arrangement is that vibrations occur within the counter-balanced arms supporting the detectors during rotational SPECT scanning resulting in the acquisition of inaccurate data.
At least one other commercially available gantry, the Elscint Apex 415 ECT, employs concepts similar to the gantry just described including having the detectors mounted a distance away from the rotation ring. A common problem resulting from these designs is that vibrations occur during rotation due to the detectors being located such a distance from the rotation ring. Additionally, for the detectors to translate the length of a patient's body an overly long translation track must be provided.
Another commercially available nuclear imaging apparatus is disclosed in U.S. Pat. No. 4,645,933 issued on Feb. 24, 1987 to Gambini, et. al. which is hereby specifically incorporated by reference. Gambini discloses a medical diagnostic system using the principles of nuclear medicine including a gantry having a detector pivotally supported by a pair of parallel support arms which are pivotally mounted to a detector support section. The support arms are weighted at the end opposite the detector for tilting rotation of the detector about an axis parallel to the arm pivot axis. One disadvantage of this configuration is that it is difficult to obtain a precise orbital rotation of the detector around a patient during an ECT or rotational SPECT scan. Also, the length of the weighted arms contributes to the creation of vibrations during rotation or translation of the detector which can result in the acquisition of inaccurate data.
One manufacturer, ADAC, mitigated the effects of vibrations occuring during rotation or translation of the detector with their Genesys system by introducing a second ring coaxial with a first ring and rotationally mounting one detector therebetween. This approach reduces erroneous data acquisition by stemming vibrations but is limited in that it is not readily adaptable for use with more than one detector because of the location of the pallet upon which a patient lies during scanning. Furthermore, it is not practically possible to have a scan performed while standing or sitting. The location of the pallet inhibits performance of scans requiring the patient to be in a position other than supine.